Dr. Seth Silbert, an ophthalmologist with Hennepin Healthcare, says a large portion of nearsightedness is due to genetics, but that can’t account for the dramatic rise in nearsightedness across the world.

“I think a lot of it is that we’re spending more time viewing objects that are close to us,” Dr. Silbert said.

He says all of the “near work” humans are doing has more of an effect on the eyes when people are young and their eyes are still growing.

“It’s more susceptible to continued expansion in its size,” Dr. Silbert says.

People see clearly when the lens of the eye focuses the light of the images at which they’re looking at the back of the eye, or the retina. For people who are nearsighted, the outer lining of the eye stretches so the eyes become too long. When that happens, the lens focuses the light on the middle of the eye, rather than the back. That makes eyesight blurry.

When people spend too much time looking closely at objects, a muscle in the front of the eye contracts. For some people, the outer lining of the eye is elastic and that contraction stretches the lining.

Dr. Silbert says tablets are more likely to have a potential impact on eyesight over reading books because kids spend more extended time staring at the electronic devices without moving them. With books, the eyes move around more when people turn the pages.

Experts say these findings don’t mean kids should read less or not use tablets. Instead, they recommend balance.

“I recommend for parents, make sure to spend lots of time playing with them, take them outside, make sure they’re engaged in activities in viewing objects at various distances,” Dr. Silbert says.

British researchers also found kids with summer birthdays were more likely to be nearsighted. That could be because they’re often exposed to reading earlier, but Dr. Silbert says some of that effect could ultimately be wiped out because children are using tablets far earlier than that.

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